The present invention relates to a PNPN semiconductor device.
PNPN semiconductor devices, also known as thyristors, have three PN junctions in series, those junctions being formed by four regions in series. The regions are an outer P-type region, an inner N-type region, an inner P-type region and an outer N-type region. The devices exhibit bistable characteristics and can be switched between a high-impedance low-current state and a low-impedance high current state.
PNPN semiconductor devices can be two-terminal devices (having connections only to the outer regions), three-terminal devices (having connections to the outer regions and one of the inner regions), or four-terminal devices (having connections to all regions).
PNPN semiconductor devices switch from the high-impedance low-current state to the low-impedance high-current state when a voltage in excess of their breakover or trigger voltage is applied to the terminals connected to their outer regions. The devices remain in the low-impedance high-current state so long as the source of the applied voltage provides a current in excess of their holding current.
The structures and the doping levels of the four regions of PNPN semiconductor devices determine the breakover or trigger voltages and the holding currents of the devices, and any one or more of those regions may include, for example, sub-regions which serve to provide breakover voltages and holding currents specific to the uses of the devices.